Generally a VDMOS has the source thereof placed over the drain, resulting in a current mainly vertical when it is on. The VDMOS has advantages of easy to drive, high commutation speed, and good efficiency at low voltages, and is widely used as switch in power management application, such as DC/DC converter and load switch. Power loss in the VDMOS is the key contribution to the overall efficiency of the circuit. The major parameters relate to the power loss are on-resistance and gate charge of the VDMOS. It would be beneficial if VDMOS having improved designs are provided.